Accurately analyzing internal conditions of a furnace is an essential task for an operator to better control temperatures of different regions in a furnace enclosure for producing products more efficiently and saving energy-related costs. Typically, image-capturing devices, such as color cameras, infrared spectrometers, filtered cameras, and the like, are installed in the furnace enclosure for detecting the temperatures of the furnace enclosure. Intensities of image pixels received from the devices have a direct relationship with the temperatures of viewed surfaces inside the furnace.
Such image-capturing devices provide a wide coverage of the furnace enclosure when compared to measurement techniques used by temperature sensors, such as thermal couples and pyrometers. Calibration is performed to establish the relationship between the temperatures and intensities. However, the furnace enclosure has different regions with large variations in surface and volume temperature. For example, certain regions, known as flame regions, are close to a heat source (e.g., a burner), and thus have higher temperatures and higher image pixel intensities when compared to other regions, known as cold regions (e.g., an exhaust area), where the image pixel intensities are relatively lower.
Typically, the regional temperatures of the furnace enclosure can vary depending on locations of the regions. An exemplary temperature value of the cold regions is approximately 300 degree Celsius (or ° C.) or 570 degree Fahrenheit (or ° F.), and for the flame regions, it is approximately 1500° C. or 2700° F. The flame and cold regions can be imaged in the field of view of the same image-capturing device. A dynamic range of each image-capturing device, which describes the ratio between the maximum and minimum measurable light intensities, depends on sensor characteristics of the image-capturing device, which in turn determines the maximum and minimum sensed temperatures and radiance based on device settings (e.g., shutter speed, aperture and gain).
An image-capturing device with a high dynamic range has a large pixel size (pixel pitch) when compared to a regular camera. The cost of a camera with high dynamic range is also much higher compared to a regular camera. However, even if such image-capturing devices are installed and used in the furnace, captured images may be overexposed in one region and/or underexposed in another region due to large variations in temperature and corresponding radiation. As a result, detailed temperature profiles of the overexposed and/or underexposed regions become undetectable or unmeasurable as excessively bright or dark areas. These regions, herein, are referred to as poor responsive regions. Recovering the detailed temperature profiles of these regions is impossible because a limited number of bits per pixel is insufficient to represent a possible temperature range.
Therefore, there is a need for an improved method of providing detailed temperature profiles of the full furnace region and ensuring that overexposed and underexposed regions of the furnace enclosure do not occur while imaging a combustion process of the furnace.